In the conventionally well known employed hydrotreating processes for hydrocarbon oils produced from crude oils or coals, catalysts are used. The catalysts are composed of inorganic oxides, for example, alumina carrier substances carried on active metal elements including cobalt, nickel, molybdenum, tungsten, or the like. These types of catalysts are normally prepared by means of the follow consecutive processes; namely, forming alumina hydrates, sintering of .gamma. alumina carrier substances, impregnating them with aqueous solutions of active metal salts of cobalt, nickel, molybdenum, tungsten or the like, drying at about 100.degree. C., and calcining the impregnated carrier substances at temperatures ranging from 400.degree. to 600.degree. C.
Since the carried active metal elements are formed as oxides in the above prepared catalysts for hydrotreatments, then they can not be utilized as-prepared due to relatively low catalyst activity. Hence, in order to add the activity of hydrotreating to the catalysts prior to usage, the catalysts are filled in a reactor column, through which light oils containing sulfurizing agents is purged under flowing hydrogen to conduct a presulfurization treatment in order to convert the oxides of active metal elements impregnated in catalysts to sulfides. This is followed by replacing the light oils to operating oils for the purpose of conducting normal operations.
However, it has been noticed that the conventionally prepared catalysts can not satisfactorily meet an ever-growing demand on reducing the levels of sulfur or nitrogen compounds in the heavy oils or the like from a viewpoint of environmental protection. Although, several catalysts exhibiting high activity have been previously investigated, none of these catalysts have been evaluated to be practically suitable.
For example, an improved treatment has been disclosed in the Japanese Patent Application Laid Open Tokkai-Hei No. 1-148347. However, in measuring the activity of, hydrogenating catalyst, no catalyst for desulfurization or denitrogenation was enhanced. According to the improved pretreatment, by using 0.degree.-50.degree. C. aqueous or organic solutions of reducing agents properly selected from a group consisting of aldehydes having 2-14 carbon atoms per one molecule, alcohol or polyhydric alcohol that contain 1-14 carbon atoms per one molecule, or organic acid or polyacids having 1-14 carbon atoms per one molecule, the catalysts which are carried with at least one type of elements from the Group VIII metals in the periodic table thereon are impregnated with said reducing agents in such a way that the reducing agent is to be impregnated at 10 ppm-100 weight %. The thus impregnated catalysts are further pressurized under 1-10 barr and heat treated at 100.degree.-150.degree. C. to promote the reduction reaction and dry. However, according to example 1 disclosed in the Laid Open document, it was found that the selectivity and activity of the activated catalysts of the aforementioned application were evaluated to be similar to the selectivity and activity of activated catalysts prepared by the conventional methods, and the end result is that there is no significant improvement to be noticed.
Moreover, a preparing method for highly activated catalysts for desulfurization was disclosed in U.S. Pat. No. 4,530,917. According to this patent, catalysts prepared through the conventional methods were impregnated with organic solution which was produced by dissolving organic sulfur compounds into light oil, aldehyde, ketone, polyketone, alcohol, organic acid, polyacid or the like. The thus impregnated catalysts were furtherly heated under flowing hydrogen gas to complete the activation reaction of the catalysts at relatively lower temperature region.
However, since the catalysts are calcined at 500.degree.-550.degree. C., which is a similar condition as a conventional method, active metal elements carried on the catalysts are in the form of oxides and this enables them to bond strongly with the carrier substances. Hence, even when the sulfurization agent is added to catalyst surfaces with the aid of an organic solvent, an improvement of the dispersibility of active metal elements in the catalysts can not be expected in spite of the fact that the activation initiation temperature can be lowered than that for the conventional method. Accordingly, the hydrotreating activity is evaluated to be of no difference from that method when the calcined catalysts are used without said organic sulfur compounds, so that in consequence hydrodesulfurization and hydrotreated denitrogenation reactions can not be promoted. No description to overcome these problems can be found in the above cited patent document.
Furthermore, the Japanese Patent Application Laid-Open Tokkai-Hei No. 4-210240 has disclosed a presulfurization method by which an .gamma. alumina carrier substance is impregnated with an aqueous solution of active metal salts including cobalt, nickel, molybdenum, tungsten or the like. The catalysts which were subjected to only drying are filled into a reactor column to which hydrogen gas containing hydrogen sulfide is introduced to presulfurize the catalyst at 400.degree. C. for a certain period of time, so that the activity for the hydrocracking can be enhanced. However, the aforementioned application includes a description of only the hydrogenation and hydrocracking of the model compounds. It does not describe the method by which the ability of hydrodesulfurization or hydrodenitrogenation of hydrocarbon oils would be altered, nor what type of additives can promote the reaction by which hydrodesulfurization or hydrodenitrogenation can be achieved.
Moreover, the Japanese Patent Application Laid-Open Tokkai-Hei No. 4-166233 discloses a preparing method of the catalysts in which, after an impregnation process of active metal elements to .gamma. alumina carrier substance, alcoxycarboxylic acid was added to catalysts which was dried or calcined after drying, followed by drying employing temperature below 200.degree. C. According to an example described in the aforementioned application, although the catalysts prepared by the method exhibited a higher reaction velocity constant than catalysts manufactured through the conventional method; it was only when the methoxy acetic acid is utilized as one type of alcoxycarboxylic acid did the prepared catalysts exhibit about a 2 times higher relative activity constant compared to catalysts prepared by the conventional method. However, even if the methoxyacetic acid is employed to improve the relative activity, the relative activity itself does not even reach the satisfactory level expected.
Furthermore, by a method with which the aforementioned methoxyacetic acid is utilized, both drying the .gamma. alumina carrier substance after being impregnated with active metal elements at 110.degree. C. for 5 hours and drying the substance impregnated with the alcoxycarboxylic acid at 110.degree. C. for 10 hours are absolutely necessitated, so that the reduction of the productivity of catalysts can by no means be avoided. It is prone for the carboxylic acid as one type of strong corrosive acetic acid to produce during the presulfurization process by using hydrodesulfurization catalysts prepared by the aforementioned method, causing undesired damage of equipment and consequently shorten the system life.
Furthermore, according to said Japanese Patent Application No. 4-166233, it was described that an improvement of the activity can be achieved as a result of a controlled agglomeration of the active metal element on the catalysts carrier substance by forming complex ions composed of said alcoxycarboxylic acid and active metal elements. Hence, it is suggested that the method described in the above cited patent specification is due to the formation of complex ions. Namely, alcoxycarboxylic acid plays an extremely important role in that method and is an indispensable additive. Moreover, no concrete description on hydrodenitrogenation is described in the application.